Here are some of my thoughts on how to achieve a PLB-doable version of the inspiration below.

The tri-color that runs vertical on the AE86 is cool but will be cumbersome. I would focus more like the Celica and concentrate on some easy vertical (angled) vinyl. Dont try to keep the white space in between like the Celica just butt the colors right up to each other like the AE86

The thick rub-rail/door guard/body trim that runs the middle of the MR2 door is going to cause hassle with either paint or vinyl. I would concentrate the tri-colors only to the area above that body line. This way the vinyl would start at the top of the body line and continue right up to the window trim.

From the point of the rearmost of that rub-rail (under the gas cap) to the rear-most of the c-pillar I would recommend the last of the vinyl. This will keep the vinyl off the complex curve of the wheel-lip/fender flare. Everything after there would be a long section of white in paint. The reason for paint is that I bet paint will do an easier job to get the fender flare.

So, from the rear, white paint to about the gas cap. This will be painted first. Once dried enough and angle of yellow vinyl, an angle of orange vinyl and finished with an angle of red. The red should not touch the front fender but rather begin on the door (sort of similar to the Celica)

I think with white vinyl magnet you should make your own 98 number panel (like shown above on the Celica). Use magnet because then, after the event taking off the GRM number panel wont ruin your vinyl. GRM does allow for reserved numbers and the use of your own number panel as long as it is legible.

Now, under the body line/rub-rail you are left with a large open black spot. This would be a cool area to add a Toyota logo like shown above on the AE86, but... Since you have not used the GRM number panel and the name GRM is not shown on the car, the easy fix here would be to apply a GRM window decal to this are and thereby represent GRM.

I have no photoshop skills. Maybe Gameboy can whip something up off these idea

The entire front clip of the car will remain black so to break that up a bit some tri-colors should be added to the hood if possible. Would also be cool if this finished with another white sheet magnet number panel. Inspiration:

I've been thinking about the actual build part of this, and I think the way to go (assuming things don't just melt down into chaos) will be to have two main groups, we'll call them A and B. So the overview of the build would look something like this:

People can jump between the two groups at will but having the distinction between them will probably help a lot at the beginning. We may want to have designated runners for parts/fluids/paint/food/drink as well as a person documenting, both would be separate from these groups.

We'll probably also want a piece of cardboard with two wishlists for "stuff" and "people" that we can add to and keep on display for people to jump in. So 6 hours in it might say:
"Stuff: CV grease, JB weld, gear oil"
"People: Wiring wizard, aluminum TIG expert (BYOW)"